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October 8, 2007

Keep package in place during reflow

I have a build-to-print job that requires LEDs and photodiodes in clear SOT23 packages to be precisely placed on the board in all three dimensions. Currently when the boards go through the reflow oven the photodiode packages float on the solder and end up 10 to 15 mils up off the board. Is there a method to keep them in place and in contact with the board as they go through the oven? We do not have a glue machine.

D. H.

Expert Panel Responses

You have already answered your own question. Placing a small amount of adhesive under the body of the component, will secure it to the substrate prior to reflow and insure the X, Y and Z position does not change. Most surface mount adhesives cure around 100 degrees c, this is just before the flux in the solder paste becomes active and well before the metal becomes liquid, insuring the component will not move during reflow. Adding a glue machine to the line is one option, however, many placement machines today also have adhesive dispensing capabilities precisely for this reason. Machines that have dispensing options include, the Fuji NXT and Fuji XPF placement systems.

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Scott Wischoffer
Marketing Manager
Fuji America Corporation
Scott Wischoffer has been in the SMT industry since 1986 with experience in service, training, sales & applications, and marketing.

The only way to secure them is with an adhesive. While you mention you do not have a glue machine, you can purchase a hand dispenser for SMT adhesive for well under $400.00USD. Once the parts are secured, you will be able to solder them without movement. If you prefer not to glue them, you can hand solder them post reflow.

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Edward Zamborsky
Regional Sales Manager
OK International Inc.
Mr. Zamborsky serves as one of OK's technology advisers to the Product Development group. Ed has authored articles and papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead Free Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.
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